T40G Time and Date will not update properly

Recent installation, mix of T46S and T40G Yealink phones. T46S Time and Date are fine, T40G it will not update properly.
NTP is on the 3CX system, pool.ntp.org.
Running 15.5 SP3
Cannot find any difference or reason it works fine for the one model and not the other.
T40G is on the latest firmware.

There must be a difference between them (beyond model) please confirm your full firmware version as you have just said "latest" did you download the firmware provided from 3CX when you updated to SP3 ? or download from the Yealink website directly ?

For Yealink (of any model) here is where you can check and amend your time-zone settings:

For an individual extension it can be set in the extension:
Extension >> Provisioning "Timezone"

In Parameters >> TIME_TIMEZONE_YEALINK

Is there any difference of location between the T46S and T40G's (different subnets for example).